when we are interested only in what happened rather than who or what did it:

The 24-foot python was caught in that village.

when we wish to emphasize the person or thing acted on rather than the one who did it:

John was presented with a bravery award yesterday.

when we choose not to name the one who performed the action to cover up a fault:

The work was poorly done.

when it is felt necessary to evade responsibility by some people or organization:

The family matter is being dealt with (by someone).

Reasons for not using the passive voice

The passive voice uses too many words, and at times can be difficult to understand. The active voice expresses in fewer words and is easy to understand. Writing tends to become clearer when unnecessary words are not used.

Examples:

Passive: The protesters were kicked, punched and handcuffed by the police before they were taken away in the police van. (Words:19 / Characters: 93)

Active: The police kicked, punched and handcuffed the protesters before taking them away in a police van. (16/82)